Natural gas is eco-friendly energy source playing an important role in the energy system which has been maintained without environmental disruption. Natural gas exists as natural gas hydrate in nature, which is a crystalline clathrate hydrate containing hydrocarbons such as a major component of methane, and trace amounts of ethane, propane and butane. Natural gas hydrate deposited worldwide is being noted as an alternative energy source to fossil fuel in the future, since natural gas in a form of natural gas hydrate has been reported to be stored in an amount of about 0.2×1015 to 7,600×1015 m3, which is an amount to supply most energy consumed in the world (see: Sloan, Jr. E. D., et al., Nature, 426:353-359, 1998; Lee, S. Y., Holder, G. D., Fuel Processing Technology, 71:181-186, 2001).
To maximize the utilization of such valuable natural gas hydrate as an energy source in real life, methods for dissociating CH4 from the natural gas hydrate should be explored, and several approaches have been made in the art as follows: thermal stimulation which dissociates methane from the natural gas hydrate by injecting water of high temperature to hydrate layer through a pipe; depressurization which dissociates methane from the natural gas hydrate by depressurizing natural gas hydrate layer using a vacuum device; and, injection of inhibitors which dissociate methane from natural gas hydrate by interfering the condition that natural gas hydrate exists in a stable form to change the equilibrium toward higher temperature and lower pressure (see: Gunn, D. A., et al., Terra Nova, 14:443-450, 2002).
However, in case of using the said prior methods, CH4 gas as a major component of natural gas hydrate is dissociated and released directly so that natural gas hydrate layers are disrupted, to give rise to geological problems such as a ground subsidence and environmental problems such as considerable changes in the ecosystem (see: Lelieveld, J., et al., Nature, 355:339-342, 1992).